The invention relates to a photographic camera provided with an interchangeable lens, particularly a camera of the still camera kind, as distinguished from a motion picture or cine camera.
In such cameras, the interchangeable lens has a certain position, which may be described as the first position, in which the lens is fully and completely mounted on and engaged with the camera. It sometimes happens that, through carelessness or inattention on the part of the user of the camera, an interchangeable lens placed on the camera is not fully seated in the above described first position. It may be almost but not quite in the proper position.
An object of the invention is the provision of simple, effective, and inexpensive signalling means for signalling to the user of the camera that the interchangeable lens is not properly seated. In one form of the invention, this signalling means comprises an electric light which is lit while the interchangeable lens is in process of being applied to and seated on the camera (usually by a twisting motion) and which does not go out until the lens is fully and properly engaged with the camera body and is in its above mentioned first position. Stated another way, the warning light comes on as soon as the lens mount begins to move away from its first or fully seated position. This is accomplished by providing the circuit of the signalling device with a switch responsive to the position of the lens mount, the switch being open only when the lens is in its first position, and being closed or current-conductive in all other positions of the lens.
In a further development of the invention, the circuit of the warning signal also has a second switch which is likewise responsive to the position of the lens and which is open when no lens is present on the camera and is closed at the start of the engaging or twisting movement which occurs when the lens is first applied to the camera and starts to become engaged therewith. The commencement of the attaching motion thus activates the circuit by closing the second switch, operating the warning signal during the twisting-on motion of the lens mount until it reaches the fully mounted or engaged position, whereupon the first switch opens to stop the operation of the signal.
The warning signal is preferably produced by a lamp which lights up in a striking color and is visible on a wall of the camera which lies within the normal field of view of the user when he is using the camera in the normal way. According to a modification, light from the lamp is reflected into the viewfinder of the camera so that the warning signal will be visible to the user when he puts his eye to the viewfinder.